The conveyor belt (24) of an oven system and apparatus (20) is configured into ascending and descending spiral stacks (26) and (28) to define a central cylindrical channel (62). A pair of upper and lower fans (130) and (132) are positioned within the central channel (62) to circulate thermal processing fluid in upper and lower circuits vertically through the spiral stacks and also laterally toward the inlet of the fans (130) and (132) to set up upper and lower thermal processing zones in the spiral stacks and circulation routes for the cooking medium through the spiral stacks.
